The present disclosure relates to a method for controlling the breathing gas supply to one or more breathing masks of an emergency oxygen supply device, as well as to a device for the emergency supply of oxygen for carrying out this method.
A pressurized cabin, in which a cabin pressure ensuring the oxygen supply to the passengers amid an adequate supply of fresh air is envisaged with today's common jet aircraft which have a cruising altitude of 10,000 m and more. Emergency oxygen supply systems, with which the passengers can also be supplied with an adequate quantity of oxygen when a case of decompression arises, thus a drop in the cabin pressure, are provided in order to be able to ensure the supply of oxygen to the passengers given such an unexpected sudden pressure drop at such an altitude. Such systems typically include either pressurized oxygen containers or chemical oxygen generators which lead the breathing gas or oxygen via a conduit system to the breathing masks envisaged for the supply of the passengers, in an adequate quantity. Thereby, the emergency oxygen system is to be designed such that an adequate oxygen supply to the passengers is ensured at the maximal flight altitude to be expected. In contrast, the oxygen requirement reduces with a falling altitude, since the oxygen share in the surrounding air increases.
One constantly strives to keep the quantity of oxygen or breathing gas which is to be carried along as low as possible, since it is indeed the carrying-along of oxygen, be it in pressurized containers or in generators, which entails a significant weight which must be borne by the aircraft and reduces the payload capacity. In order to achieve this, the quantity of oxygen or breathing gas which is dispensed to the breathing masks is controlled in a manner dependent on cabin pressure according to pertinent regulations. In the case of decompression, the cabin pressure largely corresponds to the surrounding air pressure which is essentially dependent on the altitude of the aircraft. The oxygen quantity which is to be fed to the passengers is a function of the cabin pressure which is a function of the altitude, is stipulated in the pertinent regulations. Thereby, one constantly strives not only to bring the oxygen quantity as close as possible to the minimum-prescribed value, in order to maintain the oxygen consumption as low as possible, but also to design technical devices which are employed as lightweight and inexpensive as possible manner.
As described in EP 2004294 B1 entitled “A Respiratory Gas Supply Circuit for an Aircraft Carrying Passengers”, it is counted as belonging to the state of the art, to control the oxygen supply to the breathing masks and which is dependent on the cabin pressure, which is to say dependent on altitude, by way of an on/off valve. The control of the oxygen quantity is effected using pulse width modulation of the on/off valve.
The disadvantage thereby is that on one hand the PID (Proportional Integral Derivative) modules necessary for the production of the pulse-width modulation signal are relatively complicated, and on the other hand the energy requirement for the actuation of the valves is comparatively high, since the valves are activated to open in very short succession, in dependence on the frequency of the pulse width modulation and need to be held in an opening manner for a while depending on the sampling degree. Accordingly, the valves must have a very high switching durability.